There isn't really any such thing as a smooth transition. There will always be a leap of faith, when the new venture isn't quite providing enough income yet starts demanding an inordinate amount of your time and energy.
I lost my job in 2001 at a time when there weren't many jobs in my industry, so I was forced into entrepreneurship. It turned out to be a great thing, because I love working for myself and I don't think I ever would have had the guts to walk away from a steady job. So I understand your concerns.
I did have an opportunity to do more what you're talking about a few years later. As I transitioned that first business to my business team I would work in that business for the morning, then go work on my new second business in the afternoon. It was great, because I was motivated to get all my work done in the morning so I could pursue my passion in the afternoon. It wasn't smooth, though. Some days I spent all my time at the first business. Some days I had to leave the first business hanging in favor of the second. And even though I have a great team in the first business it was still a leap of faith to commit myself full time to my new venture.
Now my team runs the first business and I'm full time in the second business.
It's doable. I just wouldn't ever expect it to be smooth.
If you want to set up a call I would be happy to hear more about your situation and help you think through a strategy to smooth out this transition as much as possible.